14.3.6 chainloader

Command: chainloader[--force] file

Load file as a chain-loader. Like any other file loaded by the
filesystem code, it can use the blocklist notation (see Block list syntax) to grab the first sector of the current partition with ‘+1’.
If you specify the option --force, then load file forcibly,
whether it has a correct signature or not. This is required when you want to
load a defective boot loader, such as SCO UnixWare 7.1.